1. Field of the Invention
The present invention relates to tires for motor vehicles such as automobiles, bicycles, fork-lift trucks and the like.
2. Description of the Prior Art
Tires originate in iron rings engaged with outer peripheral surfaces of wheels for preventing wear caused by contacting the ground. Due to the development of synthetic rubber, all the motor vehicles nowadays employ tires made of rubber.
The rubber tires are divided into pneumatic ones containing air therein and solid ones having no air therein. The pneumatic tires are divided into ones having tubes therein and tubeless ones. These tires each has a tread having stripes or concave and convex patterns in order to prevent the tires from spinning or sliding. There are also employed snow tires having spikes which tires are concave in or convex on the tread portions to a large extent or spike (studded tires having protrusions embedded into the tread so that the motor vehicles can run smoothly without tire on the snow.
As mentioned above, the tread of the rubber tire is hitherto devised in its shape to improve the running stability and cushion property in order to prevent tire spinning or sliding. However, the conventional rubber tire is not sufficient in running stability, especially it does not provide stability on snow.
That is, according to the conventional tires, the tires are likely to rise upward during high speed running which entails unstable running. Paricularly since the rear wheels are likely to rise upward, a tail plane or a spoiler is provided at the rear portion of the motor vehicle for preventing the tail from rising upward by utilizing wind velocity.
Inasmuch as the conventional snow tire has the convex and the concave portions which bite into the snow and are clogged by the snow, the convex and the concave portions do not function properly. Accordingly, spike tires are employed in most cases instead of the snow tires.
The spike tires can prevent the sliding of the tires even if the convex and concave portions are clogged by the snow since the protrusions from the tread bite into the snow.
However, there are such problems in the spike tire that since the protrusions always protrude from the tread, the road surface is peeled off and dispersed into the air as dust when the motor vehicles do not run on the snow. This entails generating so-called dust pollution damaging to the health of the people neighboring the road and vanishing erasing lines on the road due to damaging of the road. To overcome the problems set forth above, there is developed the spike tire employing an amorphous metal alloy whereby the protrusions are contracted when the temperature increases to a given value. However, the amorphous metal alloy is expensive and there is not always present a close relation between the temperature and the presence of the snow. Hence, the protrusions are liable to protrude from the tread even on a road having no snow thereon.